[mpact] use mpact_venv for virtual environment name

.gitignore

diff --git a/.gitignore b/.gitignore
index f383fbc..eac555c 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1 +1,2 @@
-mlir_venv/
+mpact_venv/
+/build/

README.md

diff --git a/README.md b/README.md
index ce30ce4..4bed1da 100644
--- a/README.md
+++ b/README.md
@@ -31,8 +31,8 @@
 The following commands initialize a virtual environment.
 
 ```shell
-python3.11 -m venv mlir_venv  # one time set up
-source mlir_venv/bin/activate # for each session
+python3.11 -m venv mpact_venv  # one time set up
+source mpact_venv/bin/activate # for each session
 ```
 
 ### Install build requirements